The lock case or lock housing of a combination lock typically resides inside a container, such as a safe, vault or room, with the lock front exposed outside the container. Once the lock is unlocked, the operator may open the container and thus has access to the lock housing and the lock case back cover. The back cover is typically removable with common hand tools such as a screwdriver. Removal of the back cover permits access to the inner workings of the lock and presents an additional opportunity to defeat the lock's reliability or security as well as the potential to gain unauthorized access to the container at a later time.
Various lock-on back covers have been designed; the most notable, one effectively, is a housing covering the lock housing and uses a separate key lock to secure it covering the combination lock. The back cover of a lock without a locked on back cover can be removed by anyone who may have access to the lock housing, including those without authorization to open the lock.
Pedestrian door locks, particularly offer the most prevalent instance for one without authorization to have access to the lock housing and lock cover; i.e., a combination lock is used in conjunction with a Mas-Hamilton CDX-07.RTM. lock or similar device. Anyone in the room, even if not in the possession of an authorized combination, could remove the back cover with a screwdriver. The Mas-Hamilton CDX-07 lock is available from Mas-Hamilton Group, Lexington, Ky. Other similar devices are manufactured and sold by Sargent & Greenleaf, Inc. and Lockmasters, Inc., both of Nicholasville, Ky.
To overcome this security exposure of having the back cover removed by a person who does not have the authority to operate the lock, it is desirable to lock the back cover onto the combination lock housing in such a way as to prevent its removal unless the lock is operated to unlock the lock as part of the back cover removal process. This insures that only a person in possession of the lock combination, and the authority to operate the lock may remove the back cover.